1. Field of the Invention
The present invention relates to a blade, and more particularly to a blade for establishing charges on, eliminating charges from, or cleaning an electrophotosensitive member, a transfer drum or transfer belt used in a transfer process, an intermediate transport belt, as well as a blade for smoothing charges on, eliminating charges from, or establishing charges on a developing blade used in a developing process, among others.
2. Description of the Related Art
Among chargers, there have been known corona chargers utilizing corona discharge and contact chargers. In a corona charger, since a high voltage of 4-8 kV must be applied to a wire, the wire and the case that surrounds the wire must be isolated from each other in order to prevent current leakage from the wire to the case. Thus, the corona charger has a drawback in that it is large. Also, since most discharge current flows to the case, a large magnitude of discharge is required in order to supply a required amount of current to an electrophotosensitive member. As a result, a large amount of ozone is generated, causing oxidation of apparatus components and deterioration of the surface of the electrophotosensitive member. Also, such ozone may be harmful to the human body.
In view of such drawbacks of corona chargers, contact chargers have been replacing corona chargers.
In contrast to the corona charger, the contact charger can charge, for example, an electrophotosensitive member at low voltage, thereby enabling implementation of a compact electrostatographic apparatus. The amount of generated ozone is {fraction (1/10)} to {fraction (1/100)} to that the corona charger. The contact charger is implemented as a conductive brush, a single-layer roller, a multilayer roller, or a blade, among other forms.
In the case of a brush-type charger employing a conductive brush of, for example, rayon fibers that contain carbon, combings are unavoidable, causing current leakage to other chargers. Also, bristles of the brush fan out with use, potentially causing current leakage to a peripheral element. Charging tends to become nonuniform, causing minute ruggedness in electric potential on the surface of an electrophotosensitive member and resulting in formation of white or black lines on an image.
A single-layer blade member involves a problem in that applied voltage leaks to any scratch present on an electrophotosensitive member. Since the resistance of the blade member depends sensitively on the amount of a conducting filler added to a base material, resistance control is difficult.
In the case of a multilayer blade member, such as a roller covered with a tube, the structure is complex with a resultant increase in cost.
In the case of a blade member such as a blade including a conductive base material and an insulating layer applied or bonded to the base material, when the insulating layer wears, the conductive base material may be exposed or may exfoliate. In the case of a blade including an insulative base material and a conductive layer applied to the insulative base material, the conductive layer may exfoliate. Also, cost increases as compared to the case of a single-body structure.
When a rubber blade is bonded to a metallic holder by use of a hydrophilic adhesive, rust is produced at the location where the rubber blade is bonded to the metallic holder, due to moisture in the air, so that the bonding strength decreases.
Especially, when a rubber blade containing an ion-conductive filler is used, rust is easily produced at the location where the rubber blade is bonded to the metallic holder, so that the bonding strength decreases.
Further, in the case of a blade having an insulating surface layer, a sufficient degree of electrical conduction cannot be established between a power source and an electrophotosensitive member, so that the operation for establishing charges on and eliminating charges from the electrophotosensitive member cannot be performed sufficiently.
In view of the foregoing, an object of the present invention is to provide a blade in which the adhesive connection between a rubber blade and a holder is maintained for a long period of time; in which reliable electrical conduction with a power source can be established if the rubber blade is electrically conductive; and which enables a reliable operation for establishing charges on and eliminating charges from a member to be charged such as an electrophotosensitive member.
To achieve the above object, according to the first aspect of the present invention, there is provided a blade which comprises a blade member whose one widthwise end portion is brought into sliding contact with a subject member; and a holder bonded to the other widthwise end portion of the blade member via an adhesive layer and extending in the longitudinal direction of the blade member, wherein at least a portion of an externally exposed end surface of the adhesive layer is subjected to waterproofing treatment.
Preferably, the widthwise end portion of the blade member opposite the widthwise end portion which comes into contact with the subject member is subjected to waterproofing treatment.
Preferably, the waterproofing treatment is application of a hydrophobic paint.
Preferably, at least a portion of the adhesive used for bonding the blade member to the holder is hydrophilic.
Preferably, the blade member has electrical conductivity, and comprises a base material and an insoluble conducting filler dispersed in the base material. The insoluble conducting filler is selected from the group consisting of carbon black and metal powder.
Preferably, the blade member further contains an ion-conductive filler.
Preferably, the blade member is formed in a single body by use of the base material; one thicknesswise end portion of the blade member, which comes into contact with the subject member, does not substantially contain the insoluble conducting filler; and the other thicknesswise end portion of the blade member contains the insoluble conducting filler.
Preferably, a conductive binder containing at least a hydrophobic binder and an insoluble conducting filler dispersed therein is applied such that connection is established between the holder and at least a portion of the widthwise end portion of the blade member opposite the widthwise end portion which comes into contact with the subject member.
Preferably, the volume resistance xcfx81v of one thicknesswise end portion of the blade member which comes into contact with the subject member and the surface resistance xcfx81s of the opposite thicknesswise end of the blade member satisfy the relationship xcfx81sxc2x7L less than xcfx81vxc2x7d/L, where L is the distance between the end where the conductive binder is applied and the end which comes into contact with the subject member, and d is the thickness of the blade member.
Preferably, the surface resistance of the thicknesswise end portion of the blade member opposite the thicknesswise end portion which comes into contact with the subject member is adjusted through adjustment of grain size distribution of the insoluble conducting filler contained in the blade member.
Preferably, the surface resistance of the thicknesswise end portion of the blade member opposite the thicknesswise end portion which comes into contact with the subject member is 107 xcexa9xe2x96xa1 or less.
Preferably, the blade member is formed of an insulating or semi-conductive polymeric base material.
Preferably, the blade contains an ion-conductive filler, and a layer for intercepting ions is provided between the blade member and the holder.
According to another aspect of the present invention, there is provided a blade which comprises a blade member whose one widthwise end portion is brought into sliding contact with a subject member; and a holder bonded to the other widthwise end portion of the blade member via an adhesive layer and extending in the longitudinal direction of the blade member, wherein the blade contains an ion-conductive filler; and a layer for intercepting ions is provided between the blade member and the holder.
In the blade according to the present invention, since the adhesive layer between the blade member and the holder is subjected to waterproofing treatment, the strength of the adhesive for bonding the blade member and the holder is reliably maintained for a long period of time.
The blade member according to the present invention provides advantageous effects in that the waterproofing treatment prevents a decrease in the bonding strength due to rust, and that the conductive paste or the like enables establishment of electrical conduction via the holder. Especially, the blade member assumes a single-body structure, and the portion of the blade member at which the blade member abuts a subject member (a member to be charged such as an electrophtosensitive member). Therefore, voltage leakage can be prevented to any scratch present on the subject member, and coming off of the conducting filler from the portion of the conducting member that abuts the subject member. Also, by controlling the thickness of the low-distribution-density portion, the electric resistance of the conducting member can be easily controlled. Through employment of the single-body structure, the fabrication process becomes simple, and fabrication costs reduce. Also, exfoliation of a component element is not involved. Through employment of the polymeric base material; particularly, liquid polyurethane, the blade member can be fabricated through centrifugal molding. Also, ooze of a plasticizer is not involved.
Through contact with the subject member, such as an electrophotosensitive member, the blade member of the present invention can smooth out charges on, eliminate charges from, or establish charges on the subject member. Also, a function other than an electrical one, such as a cleaning function, can be imparted to the blade member.